The present invention relates to a picture mapping system capable of taking picture of an entire agricultural field, also capable of providing some enlarged local pictures showing in detail some local portions of the field.
In order to ensure a stabilized quality and a stabilized yield for agricultural crops, it is required to establish a field management system which can constantly monitor a crop growing environment and a crop growing state, and can also control some changes thereof by converting these changes into numerical values, so as to carry out a crop cultivation management by dealing with these values. On the other hand, to investigate a crop growing environment and a crop growing state, it is effective to perform an analysis of picture data containing a large amount and various kinds of field information. Here, so-called picture data is a sort of two-dimensional information obtainable from visible and non-visible lights.
There has been known a picture taking method called aerial photographing which involves the use of an unmanned aircraft. This method has been proved to be effective in collecting a large amount of picture information since it can have a large-scaled agricultural field to be taken in only one picture. However, the aerial photographing has been associated with the following problems. That is, an operation for such an aerial photographing is sometimes restricted by a wether condition including wind and sunlight. Moreover, the photographing operation itself requires a high cost, because it requires highly skilled technicians including pilots and other skilled persons for the control and safety confirmation of various photographing equipments.
On the other hand, another picture taking method is called ground photographing. When this method is used to take picture, since a distance between a field and a camera is very short, a larger resolution can be obtained than the above aerial photographing method, thereby making it sure to obtain very detailed information including growing state of each individual crop. However, when a camera is in a position facing straight downwardly, one photo can include only a small area of field. If a two-dimensional picture of an entire agricultural field is to be obtained, a large amount of local pictures will have to be synthesized in a picture synthesizing process performed on a computer. For this reason, it is necessary to accurately measure the position and orientation of each local picture. Alternatively, it is necessary to repeat the photographing operation for several times by correctly moving a video camera a predetermined distance, with the orientation of the video camera kept constant. For example, when a video camera having a visual field of 4 m×4 m is used to take pictures of a field having an area of 1 ha (10000 m2), at least 625 pictures will have to be taken and synthesized together. As a result, if there is not an effective means for measuring the positions and orientations of the pictures taken, it is extremely difficult to move a video camera by 4 m each time (while at the same time keeping it facing in a correct direction).
Although it is possible for the ground photographing method to take a picture of an entire filed (if a video camera is positioned above the field forming an inclined line between the field and the camera), a picture taken will vary in its size depending on a distance between the camera and the field. As a result, it is necessary to correct some distortions of a picture taken, in order to avoid any possible error in an analytical process for analyzing a crop growing state.